Demo advances quantum networking

December 1/8, 2004

Researchers from the Georgia Institute
of Technology have transferred information stored in the properties of
a cloud of rubidium atoms to the properties of a single photon.

The ability to transfer information from atoms to photons is needed
for quantum computers, which use the properties of particles like atoms
and photons to compute. Quantum computer designs generally use atoms as
memory that can store information long enough to perform computations
on it, and photons to transfer information.

Quantum computers have the potential to be many orders of magnitude
faster than classical computers for certain very large problems, including
those needed to crack today's security codes. The researchers' method,
based on a 2001 proposal by researchers from the University of Innsbruck
in Austria and Harvard University, could eventually enable long-distance
quantum networks.

The Georgia researchers fired a laser through a pair of rubidium
atom clouds, causing the clouds to emit a photon that was entangled, or
linked at the quantum level, with the atom clouds. Changes to the properties
of an entangled particle instantly affects particles entangled with that
particle.

The researchers stored a bit of information in the atoms by measuring
the polarization of the emitted photon, which put the atom clouds into
a particular quantum state. The researchers' fired a second laser through
the atom clouds to cause them to emit a second single photon whose polarization
reflected the quantum state of the atom clouds.

The researchers' next steps are to develop a quantum node that
works with the wavelengths of light used in today's telecommunications
networks so that photons can travel longer distances over fiber lines,
and to make the method more efficient.

The method could be used practically in 7 to 10 years, according
to the researchers. The work appeared in the October 21, 2004 issue of
Science.